Load feeders are switching device units which are normally arranged in a switchgear cabinet on a top-hat profile rail. In this case, a plurality of load feeders are generally attached alongside one another to a top-hat profile rail. The load feeders which are arranged in a switchgear cabinet are of modular design, in order to comply with the appropriate requirements. Load feeders such as these are intended to control and switch high currents and voltages in industrial installation technology. In particular, motors, such as polyphase motors, are operated by load feeders. In this case, the load feeder is also referred to as a motor starter.
Loads, in particular motors, which are connected and disconnected by load feeders, are often connected to a superordinate control system via a fieldbus. Nevertheless, it is frequently necessary for these loads or these motors to be selectively and safely disconnected independently of the superordinate control system. These requirements result from the safety analyses of a machine or installation, described, for example, in the international standards IEC 61508 and IEC 62061.
Safe disconnection of a load feeder which is connected via a bus system by way of a safety switching element, for example a limit switch, a ripcord or an emergency-stop button, can now be initiated only via the separate wiring of the auxiliary voltage via the break contacts of the safety switching element, see FIG. 1. In this case, the local safety switching element, also referred to as a disconnection element, is connected to external connecting terminals 2 of the load feeder 1, in which case the external connecting terminals 2 must be connected by a wire to a control module 3, and this is complex.
A further alternative is represented by safe controllers and safe bus systems, but these are in a very high price category.